The problem is that management needs there to be zero slack in the system, or they don't think they're doing their job well enough. I've seen this pattern over and over:
1) a new vertical team is created, including seasoned devs and ops hands, a bulldog of a PM, maybe a business analyst and QA as well
2) the team is successful, creating a new product that legitimately brings value
3) executives want a new line of business and so spin up a new dev team, but figure they can do it on the cheap by having the old team's QA/PM/Ops folks work for the new team too.
4) this happens a few times and now we've spun out the support functions to separate teams with their own managers
5) we're back at square 0
Why do they do this? Because they need to increase "efficiency" in order to justify their existence. They're managers, after all, so they can't directly produce value. Their only hope is to increase the efficiency with which work gets done. The problem is that a maximally efficient team/system is a minimally resilient one, and there's no one in the org who thinks their job is to promote resiliency. There's also the problem that showing an "efficiency" like one guy doing the job of three is concrete and easy to prove. An increase in systems-level efficiency -- by having three people doing three jobs and therefore not blocking any of the other expensive professionals on those teams -- is seen as as theoretical and largely hokum.
I don't know that there is a solution to this really. Even bronze age militaries experienced similar dynamics, so I'm not hopeful we can solve it by doing "agile". Also, sometimes they are right: there really isn't enough ops work on a vertical team to justify a whole full-time employee, and they really can produce more value consulting for multiple teams. I find that this is rare though, and takes a special person who is adept at context-switching. Most people aren't, and I don't know of a repeatable way of training or identifying these people, so it isn't a practical strategy for big orgs who need these things at scale.